While growing actinomycetes in starch casein agar(sca) plate some look all white and powdery or white and grey while in tsa, the same cultures will look glossy and grow sticking inside the agar itself. I need help understanding why they grow so differently please. Any idea?
Different morphology is due to the variation in the nutrients provided in respective medium. TSA is rich complex nutrient medium whereas SCA is simpler defined medium, which resulted in the differentiation of growth pattern. If you want to detect the differences among the actinomycetes, you should grow all the strains in same medium and microscopic analysis will also provide information on variation among the isolates.
I strongly agree with other answers in the topic. I would like to add that the morphology also depends on which actinomycete you are culturing, because some strains look similar on SCA and TSA (but it is quite rare, judging on my experience with streptomycetes). Actinomycetes may have different morphological forms such as substrate mycelium (inside agar), aerial mycelium (outside of the agar) and even spores (e.g. Streptomyces). Furthermore, some strains may be pleomorphic even on the same medium. These bacteria may be cultured for 6-8 weeks and in this period you may observe several changes in morphology. The disadvantage is that the strains may easily become contaminated when you grow them for so long. For that reason the quality control is always advisable. So be aware of the contamination possibility in your cultures.
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